Water and Fertilizer Use Efficiency in Subirrigated Containerized Tomato

Article Water and Fertilizer Use Eﬃciency in Subirrigated Containerized Tomato

Ariel Méndez-Cifuentes 1, Luis Alonso Valdez-Aguilar 1,*, Martín Cadena-Zapata 2, José Antonio González-Fuentes 1, José Alfredo Hernández-Maruri 1 and Daniela Alvarado-Camarillo 3

1 Departamento de Horticultura, Universidad Autónoma Agraria Antonio Narro, Saltillo 25315, Coahuila, Mexico; [email protected] (A.M.-C.); [email protected] (J.A.G.-F.); [email protected] (J.A.H.-M.) 2 Departamento de Maquinaria Agrícola, Universidad Autónoma Agraria Antonio Narro, Saltillo 25315, Coahuila, Mexico; [email protected] 3 Departamento de Ciencias del Suelo, Universidad Autónoma Agraria Antonio Narro, Saltillo 25315, Coahuila, Mexico; [email protected] * Correspondence: [email protected]

Received: 19 March 2020; Accepted: 3 May 2020; Published: 7 May 2020

Abstract: Greenhouse cultivation is highly efficient in the use of water and fertilizers. However, due to intensive production, the greenhouse industry applies ample amounts of water and fertilizers. An alternative to minimize water and nutrient loss is zero-leaching systems, such as closed-loop subirrigation. The objective of the present study was to compare the water and fertilizer use efficiency in containerized tomato plants grown in a subirrigation system and a drip irrigation system. Subirrigated plants exhibited lower biomass than drip-irrigated plants. However, the amount of nutrient solution required to restore evapotranspirated water was lower in subirrigation. The yield was marginally decreased in subirrigated plants compared to drip-irrigated plants. The amount of nutrient solution required to produce 1 kg of fresh tomatoes was 22 L in subirrigation, whereas in drip irrigation, plants demanded 41 L. The total nitrogen applied through the nutrient solution was 75% lower in subirrigation than in drip irrigation, while the phosphorus, potassium, calcium and magnesium applied was 66%, 59%, 70% and 74% lower, respectively. We concluded that the subirrigation system proved to be more water- and nutrient-efficient than the drip irrigation system due to the zero leaching of the nutrient solution, the lower number of irrigation events required and the lower nutrient demand of plants.

Keywords: zero-leaching watering systems; drip irrigation; greenhouse vegetable crops; water scarcity

1. Introduction Water is one of the most important resources. It is used for household and industrial consumption, as well as for agricultural production [1]. Agricultural production systems are the largest consumers of water [2–4]; the irrigation of agricultural crops has allowed for the raising of yields and the stabilizing of food production and prices, which in turn has permitted the achievement of food security in many countries [5]. Groundwater is by far the main source of potable water (at least 50%) and water for agricultural irrigation (43%) [6]. Nonetheless, excessive use of water because of inadequate irrigation practices has caused overexploitation of aquifers, reduced water quality due to pollution and decreased groundwater tables [7,8]. Greenhouse cultivation provides food products of high quality all year round and, in terms of yield and gross income, it is highly eﬃcient in the use of water and fertilizers due to the decrease in

Water 2020, 12, 1313; doi:10.3390/w12051313 www.mdpi.com/journal/water Water 2020, 12, 1313 2 of 10 potential evaporation and the application of advanced irrigation technologies, such as drip irrigation and hydroponics [9]. However, in spite of its high efficiency, due to its intensive use and high yields, the greenhouse industry applies more water and fertilizers on a surface area basis compared to any other agricultural system, greatly contributing to the depletion and pollution of water reservoirs. Reducing the water and fertilizer amounts used for greenhouse production is thus important due to availability and pollution concerns. In fact, greenhouse growers fear the scarcity of water of good quality much more than its cost [9]. A strategy to further increase water and fertilizer use efficiency in greenhouse production is to adopt cultivation systems that collect and reuse irrigation water by using closed-loop irrigation systems [10–12]. Soil pollution in greenhouses is also an issue of utmost importance. In Europe, for example, concentrations of NO3−-nitrogen (N) up to 2000 kg 1 ha− were recorded in a 100 cm soil depth underlying commercial greenhouses [13], while in the 1 United States, reports indicated concentrations higher than 2300 kg ha− in the soil under decades-old greenhouses [14]. Vegetable production under controlled environment systems has allowed yield and quality increases due to the higher fertilizer rates and water inputs [15]; for example, N rates for some 1 containerized nursery plants range from 1067 to 2354 kg ha− per year, which is 10–15 times higher than that recommended for field crops [16]. Common practices for greenhouse production include surface irrigation systems with no recirculation of the nutrient/fertigation solution, which is not environmentally friendly [17,18]. The loss of water and nutrients in such irrigation systems is caused by high leaching rates as the water supplied surpasses the water retention capacity of the growing medium [18,19]. Unfortunately, high leaching rates are required to avoid salt buildup in the growing media. Combining high fertilizer rates with an inadequate irrigation system results in increased leaching, and thus, in increased groundwater pollution [20]. Thus, the efficient use of water is one of the fundamental factors to guarantee food production [21]. Establishing innovative irrigation water management may contribute to the mitigation of negative issues related to climate change [22]. An alternative to minimize water and nutrient loss to the environment for soilless cultivation of vegetable species is zero-leaching systems, such as subirrigation [23–25]. Closed irrigation systems are an interesting and promising method to maximize water and fertilizer use efficiency compared to conventional open irrigation systems [2,10,23], as the nutrient solution that is not retained by the growing medium is recirculated for reuse in the next irrigation event [15,17,26–28]. Subirrigation systems have been assessed for containerized greenhouse ornamental plants, which have demonstrated increased water and nutrient efficiency [15,29,30] and increased growth [12]. Nevertheless, little attention has been paid to the use of subirrigation for containerized vegetable species [31–33] such as greenhouse tomato. The objective of the present study was to define water and fertilizer use efficiency in containerized tomato grown in a subirrigation system. 2. Materials and Methods

2.1. Cultural Conditions and Plant Material The experiment was conducted in a greenhouse at Universidad Autónoma Agraria Antonio Narro, in Northeast Mexico (25◦2304200 N Lat., 100◦5905700 W Long., 1743 m above sea level). Weather data were collected from a weather station located in the greenhouse. Mean maximum, mean minimum and mean temperature for the study duration were 25.7 ◦C, 14.4 ◦C and 20.1 ◦C, respectively, while maximum, minimum and mean relative humidity were 92%, 43% and 68%, respectively. Mean seasonal 2 1 photosynthetically active radiation was 389 µmol m− s− . Solanum lycopersicum L. cv. Climstar 20 cm tall transplants with two fully expanded leaves were planted on 26 August 2017, into 13 L black polyethylene containers (one plant per container) ﬁlled with a mixture of sphagnum moss, coconut ﬁber and perlite (40%, 40%, 20% v/v) to a height of 27 cm. 1 Initial medium pH and electrical conductivity (EC) were 5.7 and 0.8 dS m− , respectively. Water 2020, 12, 1313 3 of 10

2.2. Irrigation Systems In this experiment, a subirrigation system was designed in order to compare the water and fertilizer use efficiency against drip irrigation. The subirrigation system consisted of rigid plastic trays/troughs (69 39 16 cm; length, width and height) with two 1-plant containers each. Containers × × were placed 30 cm apart within the row, and rows were kept 120 cm apart. Each tray/trough had a system of polyvinyl chloride pipes and valves for irrigation and drainage of the corresponding nutrient 1 solution, which was pumped with a 4 HP pump. Subirrigation started when the growing medium registered a moisture tension of 10 KPa measured with a tensiometer (Irrometer Model MLT, Riverside, CA, USA), with a flooding depth and duration of 15 cm and 30 min, on which the containers remained standing in the nutrient solution. The unabsorbed solution was drained back into a 200 L storage tank for reuse in the following irrigation event and renewed every 15 days. The pH of the nutrient solution was adjusted to 6.0 0.1 prior to irrigation with ± H2SO4 (0.1 N). The evapotranspirated nutrient solution was replenished with fresh nutrient solution to complete the initial volume of the storage tank. The drip surface irrigation system consisted of two emitters dispensing a total of 2 L h 1 of nutrient solution per container, and irrigation was conducted · − when the substrate moisture tension reached 10 KPa, with enough solution to achieve a 30% leaching fraction. The experimental unit for the subirrigation treatment consisted of two containers (i.e., two plants) placed on a single tray/trough. The drip irrigation treatment also had two one-plant containers per replication. 2.3. Nutrient Solutions 1 2 2+ + Basic nutrient solution contained (meq L− ): 14 NO3−, 2 H2PO4−, 8 SO4 −, 11 Ca , 9 K and 4 2+ 1 Mg (EC = 2.4 dS m− ). During the vegetative phase, the basic nutrient solution was applied at 120% concentration. However, from the blooming of the first to the third truss, the concentration of the basic 1 nutrient solution was decreased to 70% (EC = 1.7 dS m− ), and from the third to the fifth truss it was at 1 50% (EC = 1.2 dS m− ). The fertilizer-grade salts used for preparation of the nutrient solutions included: 5[Ca(NO3)2 2H2O] 1NH4NO3, MgSO4 7H2O, KNO3,K2SO4, KCl, HNO3 and H3PO4. Micronutrients · · 1 were provided as Fe-EDTA, Zn-EDTA. Cu-EDTA, Mn-EDTA, B and Mo at (in mg L− ): 3.0, 0.2, 0.1, 1.4, 0.3 and 0.1, respectively.

2.4. Plant Growth, Yield and Mineral Composition The harvest of fruits started 120 days after transplanting and was completed when the study was concluded (160 days after transplanting). The fruit was considered ready for harvest when 80% of the pericarp was red; the fresh fruit yield was calculated on a total yield basis. At experiment termination, whole plants were harvested and the roots were washed with tap water to remove excess substrate; the substrate was divided in three layers: bottom, medium and top layers (0 to 8, 8 to 16 and 16 to 25 cm of the root ball, respectively). The shoot was separated into stems, leaves and all the fruits harvested, which were then, along with the roots, dried in an oven at 70 ◦C for 72 h prior to measuring dry weight.

2.5. Tissue Mineral Analysis and Substrate pH and EC Dry plant tissues (root, shoot and fruit) were ground to pass a 20-mesh sieve (Thomas-Wiley Mill Co., Philadelphia, PA). Dry ground tissues were analyzed for total N concentration utilizing Kjeldhal’s procedure [34], while phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) concentrations were determined in previously digested ground tissues (2:1 mixture of H2SO4:HClO4 and 2 mL of 30% H2O2) with an Inductively Coupled Plasma Emission Spectrometer (ICP-AES, model Liberty, VARIAN, Santa Clara, CA) [35]. Macronutrients accumulated in the entire plant were calculated considering their concentration in the roots, shoot and fruits and the dry weight of each plant part. Substrate pH and EC were measured in an air-dried sample from the three medium layers using the 1:2 dilution method [36]. The 1:2 mixture was allowed to sit for 60 minutes and then it was ﬁltered. The pH and EC were measured using a portable ionometer (Horiba LAQUA Twin). Water 2020, 12, 1313 4 of 10

Water 2020, 12, x FOR PEER REVIEW 4 of 11 2.6. Water and Nutrient Use Efficiency 2.6. Water and Nutrient Use Efficiency Water consumed by plants was measured indirectly in both irrigation systems. In subirrigation, the volume ofWater water consumed retained by plants by the was growing measured medium indirectly wasin both calculated irrigation systems. by measuring In subirrigation, the nutrient the volume of water retained by the growing medium was calculated by measuring the nutrient solution depleted from the tray/trough at flooding termination, while in drip-irrigated plants, it was solution depleted from the tray/trough at flooding termination, while in drip-irrigated plants, it was calculatedcalculated by measuring by measuring the solution the solution dispensed dispensed through through thethe emitters when when the the leaching leaching fraction fraction was was achieved.achieved. Water consumedWater consumed throughout throughout the the study study was was usedused to to calculate calculate the the water water use efficiency use efficiency in in terms ofterms total freshof total fruit fresh production fruit production (liters (liters of of water water per per kilogramkilogram of of fresh fresh fruit fruit produced) produced) and total and total evapotranspiratedevapotranspirated water water (liters (liters of water of water evapotranspirated evapotranspirated perper plant plant throughout throughout study study duration). duration).

2.7. Statistical2.7. Statistical Design Design and Analysis and Analysis of Irrigation of Irrigation Method Method E Effectﬀect The experimentThe experiment was set inwas a randomizedset in a randomized complete complete blocks design blocks with design two with treatments: two treatments: subirrigation and dripsubirrigation irrigation systems, and drip withirrigation six two-plantsystems, with replications six two-plant per replications treatment. per Data treatment. were Data analyzed were with ANOVA,analyzed and Tukey with´ sANOVA, multiple and mean Tukey´s comparison multiple mean test comparison (p 0.05) whentest (p appropriate,≤ 0.05) when appropriate, using R Studio ≤ (v. 3.4.2.)using [37,38 R]. Studio (v. 3.4.2.) [37,38]. 3. Results3. Results SubirrigationSubirrigation caused caused lower lower plant plant biomass biomass production production than in in drip-irrigated drip-irrigated plants, plants, which which was was due to a decreasedue to a decrease in root in and root leaf and growthleaf growth as suggestedas suggested by by theirtheir lower lower dry dry weight weight (Table (Table 1). Stem1). Stemand and fruits dryfruits weights dry weights were similar were similar for plants for plants in bothin both irrigation irrigation systems (Table (Table 1).1 Fruit). Fruit yield yield was slightly was slightly but significantly decreased (9.5%) in subirrigated plants (Figure 1). but signiﬁcantly decreased (9.5%) in subirrigated plants (Figure1). Table 1. DryTable weight 1. Dry of weight plant of parts plant of parts tomato of tomato (Solanum (Solanum lycopersicum lycopersicumL.) grown L.) grown in two in two irrigation irrigation systems. systems.

DryDry Weight Weight g Per Plant g Per Plant IrrigationIrrigation System Root Root Stem Stem Leaves Leaves Fruits Fruits Total Total SubirrigationSubirrigation 32.6 32.6 65.6 65.6 252.7252.7 69.369.3 420.2420.2 DripDrip irrigationirrigation 42.4 42.4 71.4 71.4 313.2313.2 76.176.1 503.0503.0 ANOVA p ≤ 0.001 p = 0.189 p ≤ 0.041 p ≤ 0.640 p ≤ 0.027 ANOVA p 0.001 p = 0.189 p 0.041 p 0.640 p 0.027 ≤ ≤ ≤ ≤

Figure 1. Fresh fruit yield of tomato (Solanum lycopersicum L.) plants grown in two irrigation systems. Figure 1. Fresh fruit yield of tomato (Solanum lycopersicum L.) plants grown in two irrigation systems. Means were signiﬁcantly diﬀerent according to ANOVA (p 0.018). Means were significantly different according to ANOVA (p≤ ≤ 0.018). Substrate pH was lower while the EC was higher when subirrigation was applied (Table2). Nonetheless, when averaged across both irrigation systems, the pH was higher in the middle and bottom layers of the growing medium, while the EC was higher in the top layer (Table2). The amount of nutrient solution required to restore evapotranspirated water was predominantly lower in subirrigation in most of the irrigations conducted throughout the experiment, while in drip irrigation, plants demanded twice as much solution (Figure2). Throughout the study, plants in subirrigation required 38 irrigations whereas in drip irrigation there were 40 irrigation events (Figure2). Water 2020, 12, x FOR PEER REVIEW 5 of 11

Substrate pH was lower while the EC was higher when subirrigation was applied (Table 2). Nonetheless, when averaged across both irrigation systems, the pH was higher in the middle and bottom layers of the growing medium, while the EC was higher in the top layer (Table 2).

Table 2. Growing medium pH and electrical conductivity (EC) at experiment termination as affected by two irrigation systems and the root ball substrate layer of tomato (Solanum lycopersicum L.) plants.

Irrigation Systems pH EC (dS m−1)

Water 2020, 12, 1313 Subirrigation 6.65b 2.33a 5 of 10 Drip irrigation 6.77a 0.64b Growth medium layer Table 2. Growing medium pHTop and electrical conductivity (EC) at6.18b experiment termination2.53a as affected by two irrigation systems andMiddle the root ball substrate layer of tomato6.98a (Solanum lycopersicum0.84cL.) plants. Bottom 6.95a 1.07b 1 ANOVAIrrigation Systems Irrigation systems pH p = 0.014 EC (dS m p− ≤) 0.001 Subirrigation Medium layer 6.65b p = 0.031 2.33a p ≤ 0.001 Means followedDrip by irrigationdifferent letters indicate signific 6.77aant effects according to Tukey´s 0.64b multiple comparison test (p ≤ 0.05). Growth medium layer Top 6.18b 2.53a The amount of nutrientMiddle solution required to restore 6.98a evapotranspirated water 0.84c was predominantly lower in subirrigationBottom in most of the irrigations conducted 6.95a throughout the experiment, 1.07b while in drip ANOVA Irrigation systems p = 0.014 p 0.001 irrigation, plants demanded twice as much solution (Figure 2). Throughout≤ the study, plants in Medium layer p = 0.031 p 0.001 subirrigation required 38 irrigations whereas in drip irrigation there were 40 ≤irrigation events (Figure Means2). followed by different letters indicate significant effects according to Tukey´s multiple comparison test (p 0.05). ≤

FigureFigure 2. Volume 2. Volume of nutrient of nutrient solution solution required required at at every every irrigation irrigation event to to bring bring the the growing growing medium medium to containerto container capacity capacity in containerized in containerized tomato tomato (Solanum (Solanum lycopersicon lycopersicon L.) plants. plants.

WaterWater use e ﬃuseciency efficiency was was higher higher with wi subirrigationth subirrigation as as plants plants demanded 22 22 L Lof ofwater water to produce to produce 1 kg of1 freshkg of tomatofresh tomato fruit fruit (Figure (Figure3). In3). contrast,In contrast, with with drip drip irrigation,irrigation, plants plants required required 41 41L per L per kg kg (Figure(Figure3). In terms 3). In terms of total of watertotal water consumed, consumed, water water use use e ﬃ efficiencyciency was was also also higher higher withwith subirrigation as asWater plants 2020, 12demanded, x FOR PEER 76 REVIEW L per plant, while with drip irrigation, plants demanded 154 L per 6plant of 11 plants demanded 76 L per plant, while with drip irrigation, plants demanded 154 L per plant (Figure3). (Figure 3).

Figure 3. Water use efficiency in terms of fresh fruit production and total evapotranspirated water in containerized tomato (Solanum lycopersicon L.) plants grown in two irrigation systems. Means were significantlyFigure di3. ffWatererent use according efficiency to in ANOVA. terms of fresh fruit production and total evapotranspirated water in containerized tomato (Solanum lycopersicon L.) plants grown in two irrigation systems. Means were significantly different according to ANOVA.

The amounts of N, P, K, Ca and Mg applied through the nutrient solution during the whole experiment were markedly decreased in the subirrigation system (Figure 4). Total N applied was 75% lower in subirrigation than in drip irrigation (Figure 4a), while the P, K, Ca and Mg applied decreased by 66%, 59%, 70% and 74%, respectively (Figure 4b–e). Nonetheless, N accumulated in plant tissues at experiment termination was 60% lower in subirrigated plants (Figure 4a), while P, K, Ca and Mg accumulation was 61%, 47%, 66% and 56% lower, respectively (Figure 4b–e).

Water 2020, 12, 1313 6 of 10

The amounts of N, P, K, Ca and Mg applied through the nutrient solution during the whole experiment were markedly decreased in the subirrigation system (Figure4). Total N applied was 75% lower in subirrigation than in drip irrigation (Figure4a), while the P, K, Ca and Mg applied decreased by 66%, 59%, 70% and 74%, respectively (Figure4b–e). Nonetheless, N accumulated in plant tissues at experiment termination was 60% lower in subirrigated plants (Figure4a), while P, K, Ca and Mg Water 2020, 12, x FOR PEER REVIEW 7 of 11 accumulation was 61%, 47%, 66% and 56% lower, respectively (Figure4b–e).

Figure 4.FigureNitrogen 4. Nitrogen (A), phoshorus(A), phoshorus (B), (B potassium), potassium ( C(C),), calciumcalcium ( (DD) )and and magnesium magnesium (E) use (E) efficiency use efficiency in terms ofin total terms nutrients of total nutrients applied applied though though irrigation irrigation and and nutrients consumed consumed by containerized by containerized tomato tomato (Solanum(Solanum lycopersicon lycopersiconL.)plants L.) plants grown grown in in two twoirrigation irrigation systems. systems. Means Means were were significantly significantly different di fferent according to ANOVA. according to ANOVA. 4. Discussion 4. Discussion In the present study, subirrigation resulted in a 9.5% reduction in fresh fruit yield compared to Indrip the presentirrigation. study, In addition, subirrigation there was resultedalso a 16% in reduction a 9.5% reductionin total dry inweight, fresh with fruit roots yield (−23.1%) compared to drip irrigation.and leaves In ( addition,−19.3%) being there more was sensitive also a 16% to dry reduction weight reduction in total dry than weight, stems with(−8.1%) roots and (fruits23.1%) and − (−8.9%). Substrate pH and EC were affected by the irrigation system; in general, pH was lower while

Water 2020, 12, 1313 7 of 10 leaves ( 19.3%) being more sensitive to dry weight reduction than stems ( 8.1%) and fruits ( 8.9%). − − − Substrate pH and EC were affected by the irrigation system; in general, pH was lower while EC was higher in subirrigated substrates. Nonetheless, our measurements were much lower than those reported in other studies. For example, in subirrigated containerized tomato, the substrate pH and EC 1 reported by García-Santiago et al. [39] were, on average, 4.37 and 15.5 dS m− , respectively, while we 1 are reporting an average pH of 6.65 and EC of 2.33 dS m− . The lower measurements we obtained must be because we used a progressive reduction in the concentration of the nutrient solution, as we 1 started with solutions whose EC was 2.4 dS m− at the beginning of the study, whereas at experiment 1 termination it was decreased to 1.2 dS m− . The increased substrate EC in subirrigation has been ascribed to the zero-leaching system, the unidirectional flow of the nutrient solution by capillary force, the evapotranspiratory environmental demand and the nutrient solution concentration [31,40,41]. In order to avoid dangerous EC levels, García-Santiago et al. [39] suggested that the concentration of the nutrient solution has to be decreased to a point in which plant nutrient demands are met but salt buildup, and thus substrate EC, is kept to a minimum. The more acidic pH observed in the substrate in subirrigation is consistent with reports by Martinetti et al. [42] in eggplant (Solanum melongena L.), which has been ascribed to the accumulation of H+ in the substrate due to the zero leaching in subirrigation systems [43]. Previous research has shown contradictory results as to the effect of subirrigation on the yield of vegetable species. Santamaria et al. [33] reported that cherry tomato (Solanum lycopersicon var. Cerasiforme Alef., ‘Naomi’) fruit production decreased by 20% in subirrigation compared to drip irrigation, while, according to Bouchaaba et al. [2], in green bean (Phaseoulus vulgaris L. ‘Saporro’) plants the decrease in subirrigation was 33%. The reduced growth and yield in subirrigation has been attributed to the higher EC recorded in the top layer of the root ball due to salt buildup throughout the growing season, as corroborated in the present study, and to a poor distribution of moisture at each layer [2,28,40,42]. Nonetheless, according to other researchers, this does not necessarily affect plant growth since root development occurs mainly on the bottom layer [44], so roots are not exposed to the high EC [44]. In contrast, other reports have shown increased yield by subirrigation of vegetables when compared to that obtained with surface irrigation; for example, García-Santiago et al. [39] reported a 12% increase in fruit yield in subirrigated tomato plants. In the present study, tomato fruit production was decreased in subirrigated plants; however, the effect was only marginal as drip-irrigated plants had a yield only 9.5% higher. This suggests that the benefits of subirrigation can be valuable, because with such an irrigation system there was a higher water and fertilizer use efficiency with minimal impact on fruit yield. Our results showed that water use efficiency was 22 L of nutrient solution required to produce 1 kg of fresh tomato fruit in subirrigated plants. In contrast, drip-irrigated plants demanded 86% more water. In terms of total water consumed by plants, water use efficiency in subirrigation was 76 L per plant, while drip-irrigated plants demanded 103% more water. The lower water use efficiency in drip irrigation may be associated with the nutrient solution that leaches at every irrigation event, the more frequent irrigation events required and the higher amounts of nutrient solution required at every irrigation event to saturate the substrate. Garcia-Santiago et al. [39] reported that in subirrigated tomatoes, the substrate had higher total water, easily available water and non-easily available water than in the substrate of drip-irrigated plants at the end of the growing season, resulting in a higher water retention capacity and thus less irrigation events being required than in drip irrigation. Our data are consistent with those reported by Nederhoff and Stanghellini [21] as tomato plants irrigated with an open system demanded 53 L to obtain 1 kg of fresh fruits, while in a recirculation subirrigation system, plants needed 22 L to produce 1 kg of fresh fruits. Similarly, testing on eggplants, Martinetti et al. [42] reported a 32% reduction in the nutrient solution supply, although water use efficiency was similar in both subirrigation and drip irrigation systems as plants required 46.6 and 45.5 L of nutrient solution to produce 1 kg of fresh eggplant fruits, respectively. Water 2020, 12, 1313 8 of 10

In addition to the substantial improvement in water use efficiency, subirrigation allowed significant increases in fertilizer use efficiency. In the present study, there was a higher efficiency in N, P, K, Ca and Mg in subirrigated plants compared to drip-irrigated plants. This was because, considering the sum of all the nutrients applied in all the irrigations performed during the experiment, in subirrigation 5.00 g of N was applied per plant, while for P, K, Ca and Mg it was 2.10, 14.55, 13.19 and 2.51 g per plant, respectively. In contrast, in drip irrigation 19.85 g of N was applied per plant, while for P, K, Ca and Mg it was 6.28, 35.65, 44.68 and 9.72 g per plant, respectively. The higher nutrient efficiency of the subirrigation system was due to the zero nutrient solution leaching and the less frequent irrigation events required. Parra et al. [45] mentioned that, in tomato, water and nutrient savings were remarkable (32% to 45%) when the nutrient solution was recirculated, although yield was decreased. In contrast, Oztekin et al. [46] reported that there were no differences in tomato fruit yield between closed and open irrigation systems, although there was a significant fertilizer saving with recirculation. Our data are consistent with those reported by Martinetti et al. [42] in subirrigated eggplant as they reported 91% fertilizer use efficiency when plants were grown in a subirrigation system, while in drip irrigation it was an efficiency of 79%. The higher nutrient efficiency in subirrigation may also be due to the fact that plants grown under such a system are 16.5% lower in total dry weight compared to drip-irrigated plants; thus, such plants met their demands with lower nutrient contents, as they accumulated 60%, 61%, 47%, 66% and 56% lower N, P, K, Ca and Mg in plant tissues, respectively. Nonetheless, this reduced growth of subirrigated plants did not markedly impact fruit yield, which is in agreement with reports by Massa et al. [10], concluding that any fertigation strategy, such as recirculation of the nutrient solution, is capable of reducing fertilizer use without reducing yield, and therefore has a very promising effect on crop profitability. Blessington-Haley and Reed [30] also showed that subirrigation of several ornamental plants resulted in a K efficiency twice as high of that of surface-irrigated plants.

5. Conclusions Subirrigation proved to be more water- and nutrient-eﬃcient compared to the drip irrigation system for soilless greenhouse tomato production. The higher eﬃciency is due to the zero leaching of the nutrient solution, the lower number of irrigation events required and the lower nutrient demand of plants, with marginal impact on fruit yield.

Author Contributions: Data curation, L.A.V.-A.; Formal analysis, M.C.-Z.; Funding acquisition, L.A.V.-A.; Investigation, A.M.-C., L.A.V.-A. and M.C.-Z.; Methodology, A.M.-C. and D.A.-C.; Project administration, L.A.V.-A.; Resources, J.A.H.-M.; Software, J.A.G.-F.; Supervision, L.A.V.-A., J.A.H.-M. and D.A.-C.; Visualization, M.C.-Z. and D.A.-C.; Writing—original draft, A.M.-C.; Writing—review and editing, M.C.-Z. and J.A.G.-F. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: The authors thank the National Council of Science and Technology of Mexico (CONACYT) for supporting Ariel Méndez Cifuentes’ Ph.D. Scholarship and the Universidad Autónoma Agraria Antonio Narro for supporting this research. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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